The force is given by $F = -kx$, so $k = 50 \, \mathrm{Nm}^{-1}$. The mass $m = 0.50 \, \mathrm{kg}$. The time period for simple harmonic motion is:
\[ T = 2\pi \sqrt{\frac{m}{k}}. \]
Substituting $k = 50$ and $m = 0.5$:
\[ T = 2\pi \sqrt{\frac{0.5}{50}} = 2\pi \sqrt{0.01} = 2\pi \times 0.1 = 0.2\pi \, \mathrm{s}. \]
Given $T = \frac{x}{35}$, equating:
\[ 0.2\pi = \frac{x}{35}. \]
Substituting $\pi = \frac{22}{7}$:
\[ 0.2 \times \frac{22}{7} = \frac{x}{35}. \]
Simplifying: \[ x = 0.2 \times 22 \times 5 = 22. \]